1. Field of the Invention
The present invention relates to traffic processing in a packet data network, and more particularly, to a method and apparatus for dynamically managing hierarchical flows that enables more efficient processing of packet traffic while maintaining compatibility with an existing packet data network in transferring both circuit traffic and packet traffic in a packet switched network.
This work was supported by the IT R&D program of Ministry of Information and Communication (MIC)/Institute for Information Technology Advancement (IITA) [2007-S-012-01, Project Title: Multimedia Convergence Network on Chip Technology Development].
2. Description of the Related Art
In a current switched network, a circuit switched network and a packet switched network coexist. Gradually, the circuit switched network is being incorporated into the packet switched network, but the process of incorporation is slow because the two networks each have their advantages and disadvantages.
A packet switched network is mainly comprised of Ethernet and Internet Protocol (IP)-based Ethernet switches and routers. Its most serious disadvantage is that it is difficult to guarantee Quality of Service (QoS). A current packet switched network often cooperates with a multimedia network or a conventional Time Division Multiplexing (TDM)/Synchronous Digital Hierarchy (SDH) network, causing a network synchronization problem.
Several techniques for solving the QoS problem in the packet switched network have been disclosed. QoS depends mainly on traffic or bandwidth management techniques selected depending on the location and scale of the network.
For example, there is a bandwidth management method using a hop-by-hop scheme that may be used in an access network or a metro network. This bandwidth management method may be classified into a hierarchical bandwidth management method and a classification-based bandwidth management method.
The hierarchical bandwidth management method is disclosed in U.S. Pat. No. 6,795,441. The hierarchical bandwidth management method includes hierarchically assigning different bands to stages, and fairly transferring traffic transmitted and received by terminals using a scheduler guaranteeing fairness in a switch of each stage. The method is widely used because the switch in each stage can be easily managed and fairness for best effort traffic is guaranteed.
In this method, however, when congestion occurs while a terminal is using a certain bandwidth for traffic other than best effort traffic, such as a moving-picture stream, data packets may be lost in spite of the terminal using sufficient bandwidth. This problem is not very serious because real-time virtual circuit traffic occupies a smaller part of the bandwidth in the packet switched network, but it may become serious in a future circuit switched network incorporated into a packet switched network.
As an example of a method for solving this problem, a classification-based bandwidth management method is disclosed in U.S. Pat. No. 6,574,195. The classification-based bandwidth management method uses a concept of a micro flow, which will now be described in greater detail.
A switch in each stage finely classifies traffic received from respective terminals into layer 2 to upper layers depending on its attributes. The resultant flows are referred to as micro flows. The bandwidth is managed by micro flows as traffic units. This method advantageously guarantees fair aggregation, distribution and switching while maintaining traffic attributes because the switch in each stage manages the bandwidth by finely dividing traffic according to its attributes.
However, the method requires finely predefining attributes (e.g., QoS set) of flows depending on the traffic, and is incapable of compensating attributes of a damaged flow when the network cooperates with a network that uses a different bandwidth management method. The method makes management difficult because it requires newly defined flow attributes for new services.
Another hierarchical bandwidth management method, disclosed in U.S. Pat. No. 7,161,904, involves hierarchically dividing flows according to their attributes, measuring a bandwidth for each layer, and managing the bandwidth according to the measurement. This method enables management of traffic with different attributes separately or in association, but traffic management becomes more difficult as the number of flows increases.
The above problems with conventional bandwidth management methods have motivated research into new methods. One relatively simple method involves transferring real-time traffic while maintaining its attributes. In the field of a local area network (LAN) switch, residential Ethernet and an AV bridge originate from a synchronous Ethernet.
In the method, frame synchronization is performed in a network and packet delay is held constant in a switch and a bridge of each stage for QoS guarantee and network synchronization. Also, the QoS guarantee and high-definition network synchronization in the Ethernet helps solve problems associated with a conventional Ethernet. However, the method is incompatible with the conventional Ethernet and requires frame synchronization in all switches and bridges in the network.